1. Field of the Invention
The present invention relates to a lancet which is a blood collecting needle device, and more particularly to a disposable lancet.
2. Description of Prior Art
Currently, there are many types of electronic blood sugar testers available at the market and easy to use for diagnosis of diabetics. Therefore, the test of blood sugar value is now very widely and often conducted in hospitals and homes, and not only by those who are in charge of diagnosis and treatment but also by the diabetics themselves.
Many people are now concerned more than ever of the diagnosis or prevention of geriatric diseases, and consequently the blood sugar test is now done also for these purposes. The pregnant women in Europe and America take examinations of their blood sugar values at proper intervals during the period of pregnancy.
Depreciation in the selling price of the blood sugar testers has been taking place these years due to the development in technology and the competitive pricing. Such a situation is rapidly increasing the demand and delivery of the blood sugar testers.
The operation for that blood test may usually be executed using a marketed type of finger-pricking device in combination with a disposable lancet attached thereto. A needle protecting cap will be twisted off the lancet so that an acute needle end is exposed, before an internal spring is compressed and locked. Then the device's front end will be pressed against a finger tip from which a blood sample is to be taken, and thereafter the spring will be unlocked to thereby cause the needle end to pierce the finger tip. A small cut is made in this way so that a little amount of blood is sampled from the pricked finger.
Generally, the lancet is replaced with a new one every time when a new blood sample is taken. The used and detached lancet will be discarded with safety using the needle protecting cap which has been twisted off the lancet body. In detail, the cap will be thrust with the used needle end which protrudes from the lancet body (by a distance of about 2.8-3.3. mm and varying between the marketed models) before it is thrown away.
Such a prior art lancet 1 is diagrammatically shown in FIG. 1 and comprises a lancet body 5 and a needle protecting cap 7. To use this device, the cap 7 will be twisted off the lancet body 5 at first to expose its needle end 3.
After use, a side portion of the cap 7 is thrust with the needle end 3 so that this end 3 remains within the cap when and after discarded.
The material forming the protecting cap is usually a linear-molecule low-density polyethylene which is so soft that it can be easily and readily thrust with the needle end.
Twelve typical models of lancets on the market have their needle ends protruding from their lancet bodies by a distance of from about 2.8-3.2 mm. The maximum thickness T.sub.1 of the needle protecting caps falls within a range from about 3.8-4.0 mm. Thus, the pointed end of any needle piercing the cap from its one side surface may not jut from its other side surface.
The needle or canula will not usually tend to drop off the cap which it has pierced, since the compressive elasticity of the cap grips the needle.
The force required to pull the needle off the cap which it has pierced depends on the length of needle end exposed out of the lancet body. The longer the needle end, the stronger is the force needed to withdraw it.
The present inventor has carried out a measurement to know the relationship between the exposed length of the needle end (which length is substantially equal to the pierced depth of the cap) and the force needed to withdraw the needle end from the pierced cap. The twelve typical models referred to above were subjected to this measurement (in which five samples were tested for each model). As a result, it was confirmed that the force to withdraw the needle end was 400-500 grams for the shortest needle ends protruding 2.8-2.9 mm, and in contrast with this data, the force of 800-880 grams for the longest needle ends protruding 3.2-3.3 mm.
As was foreseen, the needle end which did not perfectly pierce the cap could be withdrawn with a much weaker pulling force.
This data indicates that, in accordance with the current practice, any needle end used to take a blood sample and pierce the protecting cap can be discarded safely only in a case wherein the protruding length of said needle end is sufficient, and/or the protruding length is fully caught by and fixedly held in the cap, and/or most carefully handled after piercing the cap. If such a condition is satisfied, then the used needle would never be exposed again to the outside and never come into contact with any other person.
In other words, any needle end used to take a blood sample and pierce the protecting cap cannot be discarded safely if the protruding length of said needle end is not sufficient, or the protruding length is not fully caught by and fixedly held in the cap, or not carefully handled after piercing the cap. In such an event, the used needle would possibly be exposed again to the outside and would probably contact other persons.
The hematogenous infection of virus of AIDS (Acquired Immune Deficiency Syndrome) or virus of B-hepatitis is becoming nowadays a serious problem. In the event that a lancet is used to take a blood sample from a carrier of such a disease and thereafter the lancet's needle comes into contact with any other person, this person will catch the carrier's disease.